If the DataKeeper default bitmap location (%ExtMirrBase%\Bitmaps) is not located on high-speed storage, you should move the bitmaps to a high-speed storage device in order to eliminate I/O bottlenecks with bitmap access. To do this, allocate a small disk partition, located on the high-speed storage drive, on which to place the bitmap files. Create the folder in which the bitmaps will be placed, and then Relocate the bitmaps (intent logs) to this location.
Disk Partition Size
The disk partition size must be big enough to contain all bitmap files for every mirror that will exist on your system. Each bit in the DataKeeper bitmap represents 64 KB of space on the volume, so to determine the bitmap size for a bitmap file, use the following formula:
<volume size in bytes> / 65536 / 8
For a 765 GB volume, convert the 765 GB to bytes
765 * 1,073,741,824 = 821,412,495,360 bytes
Divide the result by 64K (65,536 bytes) to get the number of blocks/bits
821,412,495,360 / 65,536 = 12,533,760 blocks/bits
Divide the resulting number of blocks/bits by 8 to get the bitmap file size in bytes
12,533,760 / 8 = 1,566,720
So a mirror of a 765 GB volume would require 1,566,720 bytes for its bitmap file, or approximately 1.5 MB.
A simple rule of thumb to use is that each GB of disk space requires 2 KB of bitmap file space.
Remember to reserve room for all mirror targets (if you have multiple target systems, each one needs a bitmap file). Also remember to reserve room for all mirrored volumes.
Handling Unmanaged Shutdown Issues
Unmanaged shutdowns due to power loss or other circumstances force a consistency check during the reboot. This may take several minutes or more to complete and can cause the drive not to reattach and can cause a dangling mirror. Use the ioAdministrator console to re-attach the drives or reboot the system again and make sure the check runs. For further information, refer to the ioXtreme User Guide for Windows.
- Check the Network Interface configuration settings. Increasing the Receive and Transmit buffers on the interfaces often improves replication performance. Other settings that may also affect your performance include: Flow Control, Jumbo Frames and TCP Offload. In certain cases, disabling Flow Control and TCP Offload can result in better replication performance. Enabling larger ethernet frames can also improve throughput.
- Check the location of the NICs on the bus (the slot that they’re physically plugged into) as this can also affect the speed.
- Use Iometer, an I/O subsystem measurement and characterization tool available free on the internet, to test network throughput. Iometer can be set up in a client/server configuration and can test network throughput directly. Another alternative is to set up a file share using the replication IP address, and then copy large amounts of data over that share while monitoring the network throughput using Perfmon (Network Interface / Bytes Sent Per Second) or the Task Manager “Networking” tab.
- Make sure you have the latest drivers and firmware for the network adapters.
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